Auto-loading rifles generally employ the energy produced in firing a round to cycle a bolt assembly (bolt carrier and bolt) and load the next round. This includes machine guns and semi-automatic rifles and handguns of many types.
One type of system for transferring energy to the bolt employs the gas pressure developed behind the bullet in the barrel upon discharge. This is know as a direct-gas operated system. A small lateral vent hole is provided in the barrel (usually at a forward location), and the momentary gas pressure is transmitted through the vent hole back to the bolt assembly to cycle it. In direct-gas-operated rifles (such as an M16 or M4 rifle) the gas pressure is transmitted via a tube that extends back to the bolt, which has a piston-like portion to which the gas imparts pressure. In others (such as an M14) the gas pressure enters a cylindrical chamber, where a piston connected via a rod transmits the force back to the bolt assembly. This may either push the bolt assembly so that the rod and bolt assembly initially move together, or the rod may “tap” the bolt assembly, providing an impulse to move the bolt assembly rearward in its cycle.
A significant concern with all types of direct-gas-operated rifles is the fouling caused by the carbon and other contaminants generated during firing. The combustion gas used to cycle the action contains sooty particles that tend to coat the surfaces they contact. In a gas-operated system, this gas is exhausted into the action, so that the bolt assembly and trigger mechanism may become fouled, and so that the chamber into which cartridges are loaded becomes coated with the contaminants. This reduces dimensions, and increases friction, leading to stoppages caused by failures to chamber a round, and failures to extract spent casings.
In piston-operated systems, the action remains free of gas fouling, but the piston itself becomes fouled. The piston requires a close fit in the gas cylinder, and fouling tends to accumulate on the cylinder and piston surfaces, creating excess friction and interference that can prevent operation. Because the chamber formed by the cylinder is essentially a dead-end that does not let the gas and particles flow through, the fouling tends to accumulate there, maximizing the problem.
The fouling generated by either gas system is stubborn in its resistance to cleaning, which creates a significant regular cleaning chore, especially for military troops in the field.
The present invention overcomes the limitations of the prior art by providing a firearm having a body with a bolt assembly reciprocating within the body. A barrel having a bore extends from the body. A gas block with an elongated chamber is connected to the barrel, and a gas passage connects the barrel bore to the gas block chamber. An operating rod has a forward end portion closely received in the gas block chamber and a rear end positioned to operably engage the bolt assembly. The gas block chamber has a forward portion closely receiving the forward end portion of the rod, and the gas block chamber has a rear portion with a profile larger than the forward portion. The forward portion of the rod may be a cylinder, and the rear portion of the gas block chamber may be fluted to provide clearance for flushing out contaminants. The rod may rotate freely to prevent accumulation of contaminants.